ESA 9150: 1967, the first electronically controlled balance wheel movement, date, running at 21,600 BPH.In addition, many watch companies employed Dynotron movements in their watches. Judging by the number of watches that are still around today, running quite happy with these movements, the Dynotrons must have been a very successful movement for ESA. These were not the first movements with a transistor the Bulova Accutron can claim that but the ESA 9150 Dynotron, launched in 1967, was the first movement with a balance and a transistor. The Bulova Caravelle 12 OUCD movement is the same as the Citizen X-8. Very little is known about them but I have been sent a couple of scans of these unique movements you can find them here in the Omega section of this website. In the early 1960s, Omega experimented with transistor controlled balance wheel watches, but none were ever brought to market. You can see this quite clearly on this Nivada dial.

ATO mark either on the movement plates and / or on the dial. As a result, millions of watches carry the ATO or Lic. This system was invented, and patented, by Etablissements Leon Hatot (ATO) in the early 1950s. When the balance swings back due to the spring, the trigger coil generates a reverse voltage and the transistor breaks the circuit to the impulse coil. As the fixed magnets on the balance pass over these coils, the trigger coil generates a voltage and the transistor completes the circuit on the impulse coil and the balance receives an impulse. The voltage to steer the base of the transistor is generated by induction in the trigger coil the visible coil in these watches is actually two coils side-by-side. The days of worn-out, sparking contacts were over. Sometimes the coil is on the balance wheel and the magnets are on the base plates, but it is more common to find it the other way around. Because a transistor can act as switch, these were the first battery-powered watchs that no longer needed a physical electrical contact. Transistorised Movements with Balance Wheel.

Esa 9154 service manual